Lenient Parsing of Content-Length Header When Prefixed with Plus Sign

hyper is an HTTP library for rust. hyper's HTTP/1 server code had a flaw that incorrectly parses and accepts requests with a `Content-Length` header with a prefixed plus sign, when it should have been rejected as illegal. This combined with an upstream HTTP proxy that doesn't parse such `Content-Length` headers, but forwards them, can result in "request smuggling" or "desync attacks". The flaw exists in all prior versions of hyper prior to 0.14.10, if built with `rustc` v1.5.0 or newer. The vulnerability is patched in hyper version 0.14.10. Two workarounds exist: One may reject requests manually that contain a plus sign prefix in the `Content-Length` header or ensure any upstream proxy handles `Content-Length` headers with a plus sign prefix.

Source published

7 Jul 2021 20:05:11 UTC

Source modified

3 Aug 2024 23:25:31 UTC

Observed here

23 Oct 2026 15:48:27 UTC

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CVSS 3.1 · 3.1 CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:L/I:N/A:N